(1) Field of the Invention
The present invention relates to a vacuum-type choke valve opening device wherein a choke valve provided on the upstream side of a Venturi part of a carburetor is connected to a diaphragm through links, while a vacuum chamber of the diaphragm is connected to an intake manifold through a passage having a vacuum delay element such as a throttle. More particularly, the invention pertains to a carburetor choke valve opening device having an altitude compensating function, wherein another passage having another delay element is connected to the vacuum chamber of the diaphragm and further connected to a control chamber separated from a vacuum chamber by a changeover valve adapted to interlock with a bellows of a conventional bellows type altitude compensator, while the vacuum chamber is connected to the intake manifold.
(2) Description of the Prior Art
As is generally known, such various valve opening devices have been developed and employed for smoothing the starting of automobile engines under a cold state as having a choke valve provided on the upstream side of a Venturi part in order to shift a rich air-fuel ratio at starting to a normal air-fuel ratio after starting.
Such a device has been employed for reliably opening the choke valve after starting, with the starting taken as a trigger, that, as shown in FIG. 1, the vaccum in an intake manifold 11 is introduced through a passage and applied to a diaphragm 8 through a vacuum delay valve such as a throttle valve 13 so as to be an actuator for actuating a link 53 to open a choke valve 4.
The choke valve opening device of the type mentioned above, however, has the following problems, since it is designed on a basic condition of the normal cold engine starting at a level land, i.e., the cold engine starting under an atmospheric pressure at a level land.
Since the intake manifold is communicated with the atmospheric air when the engine is in an operative state, the intake manifold is naturally affected by the atmospheric pressure. Therefore, the intake manifold vacuum under a low atmospheric pressure at a highland is lower than that under an atmospheric pressure at a level land.
Accordingly, at the cold engine starting at a highland, there is a corresponding delay in the operation of the vacuum sucking force in the vacuum chamber of the diaphragm through the delay element. In consequence, the choke valve is opened later at a highland than at a level land, so that the period during which the air-fuel ratio is over rich is longer correspondingly. Thus, there is such a shortcoming that the engine is unstable in idling. Moreover, there is such a problem that the exhaust emission control cannot be smoothly effected.